1. Field of the Invention
The present invention relates to the preparation of dialkyl ketones by a ketonic decarboxylative coupling of aliphatic carboxylic acids. More particularly, the present invention relates to the preparation of diethyl ketone by a ketonic decarboxylative coupling of propionic acid.
2. Description of the Prior Art
It has been shown that ketones can be formed via ketonic decarboxylation of carboxylic acids. For example, in an article in ZH. OBSHCH, KHIM., 30, 9, 2789 (1960), Rubinshtein et al, discussed the use of ThO.sub.2, CeO.sub.2, CaCO.sub.3, BaCO.sub.3, ZnO.sub.2, and CdO as active catalysts for ketonization and the vapor-phase catalytic ketonization of acetic acid over carbonates of alkaline earth metals (Ca, Ba, Sr, and Mg). In KINET. KATAL., 2, 2, 172 (1961), Yakerson et al. investigated the kinetics of the thermal decomposition of lithium, sodium, and barium acetate to ketone and used the data to specify the mechanism of the vapor-phase ketonization of acetic acid and its decomposition to methane. In KINET. KATAL., 2, 6, 907 (1961), Yakerson et al. discussed the kinetics of vapor-phase catalytic ketonization of acetic acid over TiO.sub.2, ZrO.sub.2, SnO.sub.2, CeO.sub.2, and BeO. In IZV. AKAD. NAUK SSSR, No. 1, 83 (1966), Yakerson et al. discussed the catalytic ketonization of acetic acid over a mixed binary catalyst system of ZrO.sub.2 --Al.sub.2 O.sub.3. In ZH, PRIKL. KHIM., 50, 2126 (1977), Shmelev et al. reported that diethyl ketone could be prepared by the ketonization of propionic acid in the presence of a catalyst of manganese dioxide supported on silica gel. In Japanese Publication Kokai Patent Application No. Sho 57(1982)-197237, Matsuoka discussed the preparation of a molecule of ketone from two molecules of a carboxylic acid over such catalysts as barium oxide, calcium oxide, lithium oxide, alumina, chromium oxide, manganese oxide, thorium oxide, gallium oxide, indium oxide, and oxides of various rare earth elements, which catalysts provide low conversions and selectivities, and disclosed the preparation of dialkyl ketones from carboxylic acids by means of a gas-phase contact reaction with a catalyst comprising zirconium oxide. Such catalyst can be supported on a carrier, such as alumina and silica gel. In West German Pat. No. 809,076, Godet disclosed the conversion of acetic acid to acetone in the presence of a catalyst of manganese oxide or an inorganic salt of manganese which is capable of forming an oxide by thermal decomposition, which catalyst may be deposited in fine distribution on a porous support, e.g., diatomaceous earth, glass wool, mineral wool, pumice, silica gel or activated carbon.
It has now been found that dialkyl ketones can be prepared from aliphatic carboxylic acids in the presence of a catalyst comprising manganese dioxide on alumina.